Firechecks are incorporated in a combustible fuel line and are used to protect the combustion system and its components from damage and to protect and safeguard operating personnel from injury resulting from deflagration and detonation caused by flash back. A firecheck normally includes a burner screen which prevents the passage of flame from the burner to the gas-air mixture device, and in the conventional firecheck, the flame burning on the screen will operate through a heat responsive mechanism to close a valve to shut off the flow of the combustible gas. However, under severe explosion or detonation conditions, a rapidly developing shock wave will precede the flame front and can impose damage on the burner screen and upstream equipment not designed to withstand the high pressures. Withstanding of the shock wave is the most difficult condition to meet, since many different types of combustible gas mixtures are used in industrial applications and many different pipeline configurations and pressure combinations are employed. Therefore, a firecheck, if properly designed, should withstand the extreme shockwave without damage to the burner screen or other components.
When detonation or flashback occurs, the firecheck should also provide an indication of valve closure, and the indication can be visual or a signal can be generated to actuate an alarm and/or shut down the complete system. After the cause of flashback or detonation has been corrected, the firecheck should be easily reset to its original condition.
As a further requirement, the firecheck should be designed for ease of service and maintenance. As previously noted, the shock wave from detonations can impose momentary high pressures on the screen and thus the firecheck should be designed so that the screen can be readily removed for cleaning or replacement.